Wet paper web transfer belt

ABSTRACT

The object of the present invention is to provide a wet paper web transfer belt with excellent crack resistance in the regions of the wet paper web transfer belt facing the roll edges. 
     This is achieved by an endless wet paper web transfer belt travelling by rotation while being supported by a plurality of rolls in the press part of a papermaking machine; wherein the wet paper web transfer belt has at least an outer circumferential resin layer on the wet paper supporting side, the outer circumferential resin layer comprises roll edge-facing regions positioned to face both edges in the width direction of at least one of the plurality of rolls and a central region positioned between the roll edge-facing regions, the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.5 mm or less, and the maximum profile valley depth Rv of the outer circumferential surface of the roll edge-facing regions is 40 μm or less.

TECHNICAL FIELD

The present invention relates to a wet paper web transfer belt (also referred to as transfer belt) for use in a papermaking machine.

DESCRIPTION OF THE RELATED ART

Papermaking machines removing moisture from the source material of paper are generally equipped with a wire part, a press part and a dryer part. These parts are arranged in the order of wire part, press part and dryer part in the wet paper web transfer direction.

Regarding the passing of the wet paper web in the press part, at present, closed-draw papermaking machines are known in which the wet paper web is passed in a closed draw. In the press part of the closed-draw papermaking machine, the wet paper web is transferred while being placed on a papermaking felt or a wet paper web transfer belt; therefore, there are no places in which the wet paper web travels on its own and thus the occurrence of web breaks can be prevented. Thus, closed-draw papermaking machines are advantageous with regard to high operating speeds and operational stability.

In the press part of such a closed-draw papermaking machine, press belts such as shoe press belts and wet paper web transfer belts as well as press felts are used. These shoe press belts and wet paper web transfer belts are generally press belts comprising at least 1 resin layer. The properties generally required of these press belts include flexibility, crack resistance, wear resistance, durability, dimensional stability, as well as impermeability to oil and water. One example of a material possessing all of these properties is polyurethane, which is generally used in the resin layer of the above-mentioned press belts.

Nevertheless, press belts are used under severe conditions in which they are repeatedly bent and compressed; therefore, the occurrence of cracks in the press belt surface, for example in the outer surface, is a significant problem from the viewpoint of durability. Cracks can occur inside the papermaking width of the press belt (length of the wet paper web CMD) as well as outside the papermaking width, for example in regions facing both edges of the pressing means (edge-facing regions).

In the prior art, press belts have been examined to prevent the occurrence of cracks in the above-mentioned edge-facing regions. Patent document 1 discloses a press belt which was finished so that the depth of the machining scars in the outer circumferential surface of the edge-facing regions was 10 μm or less and wherein a step was formed between the outer circumferential surface of the edge-facing region and the outer circumferential surface of the central region so that the thickness of the edge-facing regions of the press belt was smaller than the thickness of the central region.

PRIOR ART DOCUMENTS Patent Documents Patent Document 1: JP 2012-52269 A SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Even though the press belt according to patent document 1 does have the effect of crack resistance, especially when it is used as a shoe press belt wherein both edges of the shoe press belt are mounted to edge discs by fixing plates, there is the possibility of achieving the opposite effect in relation to crack resistance when it is used as a wet paper web transfer belt.

In the above-mentioned shoe press belt, both edges of the shoe press belt are mounted to the edge discs by the fixing plates; therefore, during operation of the papermaking machine, in particular during a change in the papermaking speed, the shoe press belt is susceptible to the torsional stress between its central region and edges. Thus, by making the edge-facing regions of the shoe press belt thinner than the central region and by increasing the flexural deformation at the edge-facing regions, the above-mentioned stress is absorbed and the occurrence of cracks is prevented.

In a wet paper web transfer belt, on the other hand, the edges of the wet paper web transfer belt are not fixed as with the above-mentioned shoe press belt. Therefore, in a wet paper web transfer belt, there is almost no torsional stress between the central region and the edges.

Moreover, a wet paper web transfer belt is supported at a constant tension by a plurality of guide rolls and press rolls in the press part of a papermaking machine. If the thickness of the wet paper web transfer belt is reduced at the edge-facing regions of the wet paper web transfer belt, the stiffness of the edge-facing regions will be reduced. Then, bending and curling occurs at the edge-facing regions if such a wet paper web transfer belt repeatedly passes through places where it is not in contact with a press roll, a guide roll (front side and rear side), a roll, and, due to this, there is the danger that the occurrence of cracks in these regions (including the boundaries between the edge-facing regions and the central region) is encouraged.

Consequently, the object of the present invention is to provide a wet paper web transfer belt with excellent crack resistance in the regions of the wet paper web transfer belt facing the roll edges.

Means for Solving Said Problems

The present inventors, as a result of intensive studies to achieve the above object, found out that the thickness of the regions of a wet paper web transfer belt facing the roll edges and the maximum profile valley depth Rv of the outer surface of these regions have a strong influence on the occurrence of cracks, and have thus focused their studies thereon.

Then, the present inventors found out that excellent crack resistance can be achieved by setting the thickness of the regions of a wet paper web transfer belt facing the roll edges and the maximum profile valley depth Rv of the outer surface of these regions within a predetermined range, and have thus completed the invention.

In other words, the present invention relates to the following:

(1) An endless wet paper web transfer belt travelling by rotation while being supported by a plurality of rolls in the press part of a papermaking machine; wherein the wet paper web transfer belt has at least an outer circumferential resin layer on the wet paper supporting side, the outer circumferential resin layer comprises roll edge-facing regions positioned to face both edges in the width direction of at least one of the plurality of rolls and a central region positioned between the roll edge-facing regions, the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.5 mm or less, and the maximum profile valley depth Rv of the outer circumferential surface of the roll edge-facing regions is 40 μm or less.

(2) The wet paper web transfer belt according to (1); wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is equal to the thickness of the central region.

(3) The wet paper web transfer belt according to (1); wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is smaller than the thickness of the central region.

(4) The wet paper web transfer belt according to (1); wherein a straight taper is provided from any position on the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.

(5) The wet paper web transfer belt according to (1); wherein an upward convex or downward convex curved taper is provided from any position on the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.

(6) The wet paper web transfer belt according to any one of (1) to (5); wherein the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.3 mm or less.

(7) The wet paper web transfer belt according to any one of (1) to (6); wherein the maximum profile valley depth Rv is 30 μm or less.

(8) An endless wet paper web transfer belt travelling by rotation while being supported by a plurality of rolls in the press part of a papermaking machine; wherein the wet paper web transfer belt has at least an outer circumferential resin layer on the wet paper supporting side, the outer circumferential resin layer comprises roll edge-facing regions positioned to face both edges in the width direction of at least one of the plurality of rolls, a central region positioned between the roll edge-facing regions, and edge regions positioned at the outside of the roll edge-facing regions, the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.5 mm or less, and the maximum profile valley depth Rv of the outer circumferential surface of the roll edge-facing regions is 40 μm or less.

(9) The wet paper web transfer belt according to (8); wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is equal to the thickness of the central region.

(10) The wet paper web transfer belt according to (8); wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is smaller than the thickness of the central region.

(11) The wet paper web transfer belt according to (8); wherein a straight taper is provided in any position from any position of the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.

(12) The wet paper web transfer belt according to (8); wherein an upward convex or downward convex curved taper is provided in any position from any position of the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.

(13) The wet paper web transfer belt according to any one of (8) to (12); wherein the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.3 mm or less.

(14) The wet paper web transfer belt according to any one of (8) to (13); wherein the maximum profile valley depth Rv is 30 μm or less.

(15) The wet paper web transfer belt according to any one of (1) to (14); wherein the above-mentioned at least one roll is a guide roll.

(16) The wet paper web transfer belt according to any one of (1) to (15); wherein the above-mentioned at least one roll is a press roll facing the shoe of a shoe press device.

Advantages of the Invention

Due to the above constitution, it is possible to provide a wet paper web transfer belt with improved crack resistance in the roll edge-facing regions of the wet paper web transfer belt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing one example of a running direction section of the press part of a papermaking machine.

FIG. 2 is a fragmentary sectional view showing a cross-machine direction section of the 2^(nd) press part PP2 in FIG. 1.

FIG. 3 is a cross-machine direction sectional view showing one example of a wet paper web transfer belt relating to a preferred embodiment of the present invention.

FIG. 4 is a cross-machine direction sectional view showing another example of a wet paper web transfer belt relating to a preferred embodiment of the present invention.

FIG. 5 is a cross-machine direction sectional view showing yet another example of a wet paper web transfer belt relating to a preferred embodiment of the present invention.

FIG. 6 is a cross-machine direction sectional view showing still another example of a wet paper web transfer belt relating to a preferred embodiment of the present invention.

FIG. 7 is a schematic diagram explaining a preferred embodiment of the manufacturing method (laminating step) of a wet paper web transfer belt of the present invention.

FIG. 8 is a schematic diagram showing an evaluation device for wet paper web transfer belts.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the wet paper web transfer belt according to the present invention will be explained in detail while referring to the drawings. Moreover, in the drawings, the size of each member is appropriately emphasized to facilitate explanation; this does not represent the actual size or proportion of the different members.

A typical example of the press part of a closed-draw papermaking machine will be explained based on FIG. 1. In the drawing, a wet paper web WW indicated by a broken line is transferred from left to right while being supported by a wire WF of the wire part, press felts PF1, PF2, PF3, wet paper web transfer belt TB of the press part and a dryer fabric DF of the dryer part. Thus, there are no places in a closed-draw papermaking machine in which the wet paper web is not supported by the above-mentioned papermaking equipment. The wire WF, the press felts PF1, PF2, PF3, the wet paper web transfer belt TB and the dryer fabric DF are endless belts prepared by commonly known means and are supported by guide rolls GR.

In the drawing, guide rolls GR, press rolls PR1, PR2, PR3, a press shoe PS, a shoe press belt SB and a suction roll SR are each of a known constitution. Further, the press rolls PR1, PR2 constitute a first press part PP1, while the concave press shoe PS, facing the surface (radius of curvature) of the press roll PR3, constitutes a second press part PP2 together with the press roll PR3 via the shoe press belt SB. Therefore, a relatively long press surface is formed by the second press part PP2 in the advancing direction of the wet paper web WW.

Hereinafter, the travelling condition of the wet paper web in the above-mentioned closed draw papermaking machine will be explained. Needless to say, the wet paper web WWW is manufactured continually in the direction it advances; therefore, the explanation will be in relation to one part of the moving condition of the wet paper web WW.

Firstly, the wet paper web WW passes the wire WF of the wire part, the press felt PF1 of the press part and the first press part PP1, whereupon it is passed from the press felt PF2 to the press felt PF3. Then, it is transferred to the second press part PP2 by the press felt PF3. In the second press part PP2, the wet paper web WW is compressed by the press shoe PS, via the shoe press belt SB, and the press roll PR3, while it is being sandwiched between the press felt PF3 and the wet paper web transfer belt TB.

Here, the press felt PF3 is designed to have high water permeability, while the wet paper web transfer belt TB is designed to have very low water permeability. Therefore, in the second press part PP2, the moisture from the wet paper web WW moves to the press felt PF3.

Immediately after leaving the second press part PP2, the volume of the press felt PF3, the wet paper web WW and the wet paper web transfer belt TB expands because they are abruptly released from pressure. Due to this expansion and because of the capillary effect of the pulp fibers constituting the wet paper web WW, the so-called rewetting phenomenon occurs when the moisture inside the press felt PF3 partially moves to the wet paper web WW.

Nevertheless, as described above, the wet paper web transfer belt TB is designed to have a very low water permeability; therefore, moisture is not held inside the wet paper web transfer belt. Therefore, there is almost no rewetting phenomenon occurring due to the wet paper web transfer belt TB and the wet paper web transfer belt TB contributes to improve the efficiency of the dewatering of the wet paper web. Further, after leaving the second press part PP2, the wet paper web WW is transferred by the wet paper web transfer belt TB. Then, the wet paper web WW is sucked up by the suction roll SR and transferred to the dryer part by the dryer fabric DF.

FIG. 2 is a fragmentary sectional view showing a width direction section of the second press part PP2 in the closed-draw papermaking machine shown in FIG. 1. As shown in FIG. 2, the press shoe PS and the press roll PR3 have a fixed length in the width direction. The wet paper web transfer belt TB comprises a central region A, roll edge-facing regions B, and edge regions C positioned outside the roll edge-facing regions B. Moreover, a papermaking width D in which the wet paper web travels exists inside the central region A. In FIG. 2, the wet paper web transfer belt TB is exemplified as comprising the central region A, the roll edge-facing regions B, and the edge regions C; however, the edge regions C may be omitted and a constitution comprising the central region A and the roll edge-facing regions B may be used.

The roll edge-facing region B is a region facing a site comprising the edge 21 of the press surface 20 of the press roll PR3. In the same way, the roll edge-facing region B is a region facing a site comprising an edge (corresponding to the edge 21 of the press roll in FIG. 2) of the contacting surface (corresponding to the press surface of the press roll PR3 in FIG. 2) of the plurality of guide rolls GR in FIG. 1 (not shown in the drawings). In general, the width of the press roll PR3 is equal to or less than the width of the plurality of guide rolls GR; however, the invention is not limited thereto, and it is preferred to set the roll edge-facing region B so as to comprise an edge of each roll. Moreover, in case the width of the plurality of guide rolls GR is wider than the width of the press roll PR3, the width of the wet paper web transfer belt TB may be set equal to or less than the width of the plurality of guide rolls GR. The width of the roll edge-facing regions B may for example be set between 1 cm and 40 cm, and preferably between 3 cm and 20 cm.

The shoe press belt SB is assembled in the shape of a roll as an external cylinder structure enclosing the press shoe PS. The press shoe PS is supported on a support shaft SH by hydraulic cylinders CV and can press the shoe press belt SB in the downward direction. At both edges of the support shaft SH, edge disks DI are placed by means of bearings BR. Moreover, the edges of the shoe press belt SB are bent on the outer circumference of the edge disks DI inside the radius direction; and these bent portions of the edges of the shoe press belt SB are fixed in an embodiment sandwiched by ring-shaped fixing plates PL at the external circumference portion of the edge disks DI. Consequently, the shoe press belt SB fixed to the edge disks DI can rotate while sliding on the press shoe PS. A lubricating oil is supplied between the shoe press belt SB and the press shoe PS.

The wet paper web is sandwiched between the press felt PF3, which is adjoining the shoe press belt SB, and the wet paper web transfer belt TB, which is adjoining the press roll PR3, and dewatered by the pressure applied by the press shoe PS in the direction of the press roll PR3. The width of the press roll PR3 is generally equal to or bigger than the width of the press shoe PS.

FIG. 3 is a width direction sectional view showing one example of a wet paper web transfer belt relating to a preferred embodiment of the present invention. The wet paper web transfer belt TB comprises a reinforcing fiber base material layer 31, an outer circumferential resin layer (wet paper web carrying side resin layer) 32 provided on one of the main surfaces of the reinforcing fiber base material layer 31 at the outer surface side thereof, and an inner circumferential resin layer (roll side resin layer) 33 provided on the other main surface of the reinforcing fiber base material layer 31 at the inner surface side thereof. The wet paper web transfer belt is formed by laminating these layers. The outer circumferential resin layer is the layer forming the outer surface (outer circumferential surface 322) of the ring formed by the wet paper web transfer belt TB. The wet paper web transfer belt TB comprises a central region A and roll edge-facing regions B.

The reinforcing fiber base material layer 31 is made of a reinforcing fiber base material 311 and a resin 312. The resin 312 is present in the reinforcing fiber base material layer 31 so as to fill the gaps between the fibers of the reinforcing fiber base material 311. In other words, one part of the resin 312 impregnates the reinforcing fiber base material 311, while the reinforcing fiber base material 311 is embedded in the resin 312.

There are no particular limitations with regard to the reinforcing fiber base material 311; however, for example, fabrics woven by a weaving machine and the like from warp and weft yarns are commonly used. Moreover, it is also possible to use a grid-like web material of superimposed rows of warp and weft yarns made without weaving.

The fineness of the fibers constituting the reinforcing fiber base material 311 is not particularly limited, for example, fibers of 300 to 10,000 dtex, preferably 500 to 6,000 dtex, may be used.

Moreover, the fineness of the fibers constituting the reinforcing fiber base material 311 may be different depending on the site in which they are used. For example, the fineness of the warp and weft yarns in the reinforcing fiber base material 311 may be different.

As material of the reinforcing fiber base material 311, it is possible to use one type or a combination of two or more types of a polyester (polyethylene terephthalate, polybutylene terephthalate, and the like), aliphatic polyamides (polyamide 6, polyamide 11, polyamide 12, polyamide 612, and the like), aromatic polyamides (aramide), polyvinylidene fluoride, polypropylene, polyether ether ketone, polytetrafluoroethylene, polyethylene, wool, cotton, metals, and the like.

As material for the resin 312, it is possible to use one type or a combination of two or more types of thermosetting resins such as urethane, epoxy, acryl, and the like, or thermoplastic resins such as polyamide, polyacrylate, polyester, and the like; preferably urethane resin is used.

The urethane resin used in the resin 312 is not particularly limited; however, it is possible to use, for example, urethane resin obtained by curing a urethane prepolymer having a terminal isocyanate group, which was obtained by reacting an aromatic or aliphatic polyisocyanate compound and polyol, together with a curing agent having an active hydrogen group. Moreover, it is possible to use an anionic, non-ionic or cationic aqueous urethane resin of the self-emulsification type or forced emulsification type. In this case, for improving the resistance to water, it is also possible to crosslink the aqueous urethane resin by using a cross linking agent of melamine, epoxy, isocyanate, carbodiimide, and the like, together with the aqueous urethane resin.

In addition, the resin 312 may also comprise one type or a combination of two or more types of inorganic fillers such as titanium oxide, kaolin, clay, talc, diatomaceous earth, calcium carbonate, calcium silicate, magnesium silicate, silica, mica, and the like.

The type and composition of the resin 312 in the reinforcing fiber base material layer 31 may be different in each site of the reinforcing fiber base material layer 31 or may be the same.

The outer circumferential resin layer 32 is provided on one of the main surfaces of the reinforcing fiber base material layer 31 and is mainly made of a resin material.

The outer circumferential resin layer 32 constitutes a wet paper web carrying surface (one part of the outer circumferential surface 322) for contacting and carrying the wet paper web WW on the main surface at the opposite side of the main surface that is joined to the reinforcing fiber base material layer 31. In other words, the wet paper web transfer belt TB carries the wet paper web WW on the wet paper web carrying surface (one part of the outer circumferential surface 322) of the outer circumferential resin layer 32 and can transfer the wet paper web WW.

The difference in thickness DX between the thickness DA of the central region A and the thickness DB of the roll edge-facing regions B of the wet paper web transfer belt TB is 0.5 mm or less, and the maximum profile valley depth Rv of the outer surface of the roll edge-facing regions B is 40 μm or less.

Here, the maximum profile valley depth Rv is a parameter defined according to JIS B0601:2001 (or the corresponding ISO 4287:1997). Rv expresses the maximum value of the valley depth of a contour curve over a reference length.

In case the difference in thickness DX between the thickness DA of the central region A and the thickness DB of the roll edge-facing regions B of the wet paper web transfer belt TB is 0.5 mm or less (0≦DA−DB=DX≦0.5 mm), the stiffness of the roll edge-facing regions B is maintained at the same level as for the central region A. The result is that, even if the wet paper web transfer belt TB repeatedly passes through places where it is not in contact with a press roll, a guide roll (front side and rear side), a roll, bending and curling at the roll edge-facing regions does not occur, and even if bending and curling does occur, the amount of change thereof is small; therefore, it is possible to prevent the occurrence of cracks in these regions (including the borders between the roll edge-facing region and the central region). The difference in thickness DX is preferably 0.3 mm or less, and even more preferably an equivalent thickness (in the present specification, in view of the manufacturing tolerance, a difference in thickness within 0.02 mm is referred to as an equivalent thickness) (0≦DA−DB=DX≦0.5 mm).

The outer circumferential surface 322 of the outer circumferential resin layer 32 of the wet paper web transfer belt TB is generally polished and buffed. As examples of the polishing and buffing processes, these processes may be performed by fixed polishing and buffing devices while the wet paper web transfer belt TB, which is installed on two parallel rolls, is being rotated. The result is that, in the outer circumferential surface 322, the machining scars occur in the running direction of the wet paper web transfer belt TB. If these machining scars are deep, in particular in the roll edge-facing regions B of the wet paper web transfer belt TB, the occurrence of cracks in these regions is encouraged. Therefore, the depth of these machining scars is defined by the above-mentioned Rv, and when Rv is 40 μm or less, the occurrence of cracks in these regions can be effectively prevented. And, in case Rv is 30 μm or less, it is possible to prevent the occurrence of cracks even more effectively.

It is possible to measure the above-mentioned Rv of any flat or curved surface or curved line of the outer circumferential surface 322 of the roll edge-facing regions B; however, in case polishing marks have been formed on the outer circumferential surface 322, it is preferable to perform the measurement at a right angle to the direction of the polishing marks so as to measure across the polishing mark direction.

As resin material 321 constituting the outer circumferential resin layer 32, it is possible to use one type or a combination of two or more types of resin material that can be used in the above-mentioned reinforcing fiber base material layer 31. The type and composition of the resin material constituting the outer circumferential resin layer 32 and the resin constituting the reinforcing fiber base material layer 31 may be the same or may be different.

From the point of view of mechanical strength, wear resistance and flexibility, urethane resins are particularly preferred as resin material 321 constituting the outer circumferential resin layer 32. Moreover, the outer circumferential resin layer 32 may also comprise one or more inorganic fillers in the same way as the reinforcing fiber base material layer 31. Further, the type and composition of the resin materials and the inorganic fillers in the outer circumferential resin layer 32 may be different in each site of the outer circumferential resin layer 32 or may be the same. Moreover, the outer circumferential resin layer 32 has the property of not letting water pass. In other words, the outer circumferential resin layer 32 is preferably water-impermeable.

The inner circumferential resin layer (roll-side resin layer) 33 is provided on one of the main surfaces of the reinforcing fiber base material layer 31 and is mainly made of a resin material. The inner circumferential resin layer 33 constitutes a roll-contacting surface 332 for contacting a roll on the main surface at the opposite side of the main surface that is joined to the reinforcing fiber base material layer 31. For transferring the wet paper web, the wet paper web transfer belt TB can be driven during use via a roll by bringing the roll-contacting surface 332 in contact with the roll.

As resin material 331 constituting the inner circumferential resin layer 33, it is possible to use one type or a combination of two or more types of the resin materials that can be used in the reinforcing fiber base material layer 31, as described above. The type and composition of the resin material constituting the inner circumferential resin layer 33 and the resin material constituting the outer circumferential resin layer 32 or the reinforcing fiber base material layer 31 may be the same or may be different.

From the point of view of mechanical strength, wear resistance and flexibility, urethane resins are particularly preferred as resin material 331 constituting the inner circumferential resin layer 33. Moreover, the inner circumferential resin layer 33 may also comprise one or more inorganic fillers in the same way as the reinforcing fiber base material layer 31. Further, the type and composition of the resin materials and the inorganic fillers in the inner circumferential resin layer 33 may be different in each site of the inner circumferential resin layer 33 or may be the same.

The dimensions of the wet paper web transfer belt TB described above are not particularly limited; they may be suitably set according to the use of the wet paper web transfer belt. The width of the wet paper web transfer belt TB is not particularly limited, however, it may, for example, be 700 to 13,500 mm, or preferably 2,500 to 12,500 mm. Further, the length (circumferential length) of the wet paper web transfer belt TB is not particularly limited, however, it may, for example, be 4 to 35 m, or preferably 10 to 30 m.

The thickness (thickness of the central region A) of the wet paper web transfer belt TB is not particularly limited, however, it may, for example, be 1.5 to 7.0 mm, or preferably 2.0 to 6.0 mm. In any case, the thickness should be set so that the stiffness of the roll edge-facing regions B does not decrease.

The roll edge-facing region B is set as a region facing a site comprising an edge of the press roll or the guide rolls. In general, the width of the press roll is equal to or less than the width of the plurality of guide rolls; however, it is preferred that the roll edge-facing region B is set so as to face to each site comprising an edge of each roll. Moreover, in case the width of the plurality of guide rolls is wider than the width of the press roll, the width of the wet paper web transfer belt may be set to be equal or less than the width of the plurality of guide rolls. The width of the roll edge-facing regions B may for example be set between 1 cm and 40 cm, or preferably between 3 cm and 20 cm.

Moreover, in the wet paper web transfer belt exemplified in FIG. 3, the thickness of the central region A is equal to the thickness of the roll edge-facing regions B; however, it is also possible to provide, for example, a difference between the thickness of the central region A and the thickness of the roll edge-facing regions B of 0.5 mm or less. (FIG. 4 (1)).

Furthermore, it is also possible to provide a straight taper from any position on the outer circumferential surface of the roll edge-facing region B towards the edge of the wet paper web transfer belt in the opposite direction of the central region A (in FIG. 4 (2), this position on the outer circumferential surface of the roll edge-facing region B is exemplified as the boundary between the central region A and the roll edge-facing region B; however, this position is not limited thereto, it can be set anywhere on the outer circumferential surface inside the roll edge-facing region B).

Moreover, it is also possible to provide an upward convex or downward convex curved taper from any position on the outer circumferential surface of the roll edge-facing region B towards the edge of the wet paper web transfer belt in the opposite direction of the central region A (in FIG. 4(3), (4), this position on the outer circumferential surface of the roll edge-facing region B is exemplified as the boundary between the central region A and the roll edge-facing region B; however, this position is not limited thereto, it can be set anywhere on the outer circumferential surface inside the roll edge-facing region B).

In FIG. 4, the thickness DB of the roll edge-facing regions B, as the smallest thickness inside the roll edge-facing regions B, is set so that the difference in thickness DX (DA−DB) between the central region A and the roll edge-facing regions B is 0.5 mm or less. Moreover, in FIG. 4, the right side of the wet paper web transfer belt is omitted and the left side only is shown.

Furthermore, the wet paper web transfer belts exemplified in FIGS. 3 and 4 are exemplified as wet paper web transfer belts having a central region A and roll edge-facing regions B; however, a constitution in which edge regions C are further provided at the outer side of the roll edge-facing regions B is also possible (FIG. 5).

Moreover, in the wet paper web transfer belt exemplified in FIG. 5, the central region A, the roll edge-facing regions B and the edge regions C are exemplified to be of equal thickness; however, the difference in thickness between the central region A, the roll edge-facing regions B and the edge regions C may, for example, be 0.5 mm or less (in FIG. 6 (1), a wet paper web transfer belt is exemplified in which the thickness of the edge regions C is the same as the thickness of the roll edge-facing regions B; however, it is not limited thereto, the thickness of the edge regions C may be set at will, for example, to be the same as the thickness of the central region A.)

Furthermore, it is also possible to provide a straight taper from any position on the outer circumferential surface of the roll edge-facing region B towards the edge of the wet paper web transfer belt in the opposite direction of the central region A (in FIG. 6 (2), this position on the outer circumferential surface of the roll edge-facing region B is exemplified as the boundary between the central region A and the roll edge-facing region B; however, this position is not limited thereto, it can be set anywhere on the outer circumferential surface inside the roll edge-facing region B. Further, the termination of the taper in the direction of the edge of the wet paper web transfer belt may also be in any position inside the roll edge-facing region B. Moreover, the thickness of the edge regions C may be set at will, for example, to be the same as the thickness of the central region A.)

Furthermore, it is also possible to provide an upward convex or downward convex curved taper from any position on the outer circumferential surface of the roll edge-facing region B towards the edge of the wet paper web transfer belt in the opposite direction of the central region A (in FIG. 6 (3), (4), this position on the outer circumferential surface of the roll edge-facing region B is exemplified as the boundary between the central region A and the roll edge-facing region B; however, this position is not limited thereto, it can be set anywhere on the outer circumferential surface inside the roll edge-facing region B. Further, the termination of the taper in the direction of the edge of the wet paper web transfer belt may also be in any position inside the roll edge-facing region B. Moreover, the thickness of the edge regions C may be set at will, for example, to be the same as the thickness of the central region A.)

In FIG. 6, the thickness DB of the roll edge-facing regions B, as the smallest thickness inside the roll edge-facing regions B, is set so that the difference in thickness DX (DA−DB) between the central region A and the roll edge-facing regions B is 0.5 mm or less. Moreover, in FIG. 6, the right side of the wet paper web transfer belt is omitted and the left side only is shown.

Accordingly, the wet paper web transfer belts TB relating to the present embodiments have excellent crack resistance because the roll edge-facing regions B have a prescribed thickness in relation to the central region A and the outer circumferential surface 322 of the roll edge-facing regions B have a prescribed Rv.

As a variation of the above described wet paper web transfer belts TB, an embodiment can be mentioned in which, for example, the inner circumferential resin layer is not a layer made of a resin material, but a batt fiber layer formed by needling batt fibers. Another variation of the wet paper web transfer belt of the present invention comprises a layer in which the above-mentioned resins impregnate the batt fibers. Other than the inner circumferential resin layer, these embodiments may have the same constitution as the wet paper web transfer belts TB described above. Moreover, as material of the batt fibers, it is possible to use one or a combination of two or more of the materials used in the reinforcing fiber base material 311.

Above, the present invention has been described in detail based on preferred embodiments; however, the present invention is not limited by this. Each constitution may be substituted as desired, or a constitution may be added as desired, as long as a similar function can be obtained.

Examples

Hereinafter, the present invention will be described even more specifically by means of the Examples; however, the present application is not limited to these Examples.

1. Production of the Wet Paper Web Transfer Belt

The wet paper web transfer belts of Examples 1 to 7 and Comparative Examples 1 to 3 were produced according to the method hereinafter.

(1) Resin Layer Forming Step

Firstly, the fiber reinforcing base materials and the resin materials of the constitutions described hereinafter were prepared for Examples 1 to 7 and Comparative Examples 1 to 3.

The Reinforcing Fiber Base Material

Upper warp yarn: twisted monofilament of 2000 dtex made from nylon 6 Lower warp yarn: twisted monofilament of 2000 dtex made from nylon 6 Weft yarn: twisted monofilament of 1400 dtex made from nylon 6 Weave: double warp weave of 40 upper/lower warp yarns/5 cm and 40 weft yarns/5 cm

The reinforcing fiber base material was made by entangling and integrating batt fibers of 22 dtex made from nylon 66 with the woven fabric of the above constitution by needling 100 g/m² of the batt fibers to the roll side of the woven fabric.

The Resin Material

Polyurethane consisting of the reaction product of dimethylthiotoluenediamine (DMTDA) in a mixture of tolylene diisocyanate (TDI) and polytetramethylene glycol (PTMG).

Formation of the Laminate Body

Next, with regard to Examples 1 to 7 and Comparative Examples 1 to 3, the reinforcing fiber base material was installed on two rolls 71 so that the batt fiber side was arranged on the inside, as shown in FIG. 7 (a).

Next, as shown in FIG. 7 (b), urethane resin was coated by penetrating and impregnating the fabric of the reinforcing fiber base material with liquid urethane resin from its wet paper web carrying surface side using a resin discharge device 73 and a coater bar 72 so as to form a resin layer of 1.5 to 1.6 mm thickness from the surface of the reinforcing fiber base material.

Next, the coated resin was cured and the semi-finished product of a wet paper web transfer belt was obtained, wherein a reinforcing fiber base material layer in which the reinforcing fiber base material is impregnated by urethane resin, an outer circumferential resin layer precursor formed at the outer circumference of the reinforcing fiber base material layer, and an inner circumferential resin layer formed at the inner circumference of the reinforcing fiber base material layer are laminated.

(2) Polishing and Buffing

The wet paper web transfer belts were completed by polishing and buffing the central region and the roll edge-facing regions of the wet paper web transfer belts (semi-finished products) of Examples 1 to 7 and Comparative Examples 1 to 3 and by adjusting the thickness of the wet paper web transfer belt of each Example according to the surface roughness of Table 1.

The dimensions of the manufactured wet paper web transfer belts were 20.0 m length×70 cm width (10 cm roll edge-facing region+50 cm central region+10 cm roll edge-facing region).

TABLE 1 Polishing Finishing process Thickness Roughness (rough cutting) First time Second time DA DB DX Rv Ra Device Grit Device Grit Device Grit mm mm mm mm mm Example 1 SP #120 — — — — 3.80 3.79 0.01 25 6 Example 2 SP #80 Buff Cloth buff — — 3.80 3.80 0.00 39 6 Example 3 SP #80 SP #320 SP #240 3.80 3.78 0.02 31 3 Example 4 SP #80 — — — — 3.80 3.79 0.01 39 9 Example 5 SP #80 SP #320 — — 3.80 3.79 0.01 37 6 Example 6 SP #80 SP #320 — 3.80 3.60 0.20 35 6 Example 7 SP #80 SP #320 — — 3.80 3.40 0.40 36 6 Comparative SP #60 SP #320 — — 3.80 3.20 0.60 43 15 Example 1 Comparative SP #40 SP #320 — — 3.80 2.80 1.00 46 9 Example 2 Comparative SP #80 SP #320 — — 3.80 2.40 1.40 37 6 Example 3 SP: Sandpaper polishing (belt polishing) Buff: Buff polishing (disk polishing) DA: Thickness of the central region of the wet paper web transfer belt DB: Thickness of the roll edge-facing regions of the wet paper web transfer belt DX: Difference in thickness DA − DB Rv: Maximum depth of the outer surface of the roll edge-facing regions Ra: Arithmetic average roughness of the roll edge-facing regions

2. Evaluation of the Wet Paper Web Transfer Belts

A wet paper web transfer belt was installed in the evaluation device for wet paper web transfer belts shown in FIG. 8, and after running the wet paper web transfer belt under the conditions described hereinafter, the occurrence of cracks in the outer circumferential surface of the roll edge-facing regions of the wet paper web transfer belt was evaluated.

Test Conditions

Test speed: 1200 m/min Test duration: 120 hours Pressure: 100 kN/m Tension: 7 kN/m Shower amount: 20 liters/min/m² (outer and inner circumferential surfaces) Press roll PP4 width: 60 cm Press roll PP5 width: 60 cm Guide rolls GR width: 100 cm Press roll PP4 diameter: 70 cm Press roll PP5 diameter: 70 cm

In this test, the wrap angle of the wet paper web transfer belt to the press roll PR5 was set at 90°, and the load tests of the wet paper web transfer belts were performed so that the edges of the press rolls PR4 and PR5 were in the roll edge-facing regions of the wet paper web transfer belts. The occurrence of cracks is shown in Table 2.

TABLE 2 Occurrence of cracks Boundary between the central Roll edge-facing region and roll edge-facing region regions Example 1 No cracks No cracks Example 2 No cracks No cracks Example 3 No cracks No cracks Example 4 No cracks No cracks Example 5 No cracks No cracks Example 6 No cracks No cracks Example 7 No cracks No cracks Comparative Cracks occurred Cracks occurred Example 1 Comparative Cracks occurred Cracks occurred Example 2 Comparative Cracks occurred No cracks Example 3

During the tests, bending was confirmed along both edges of the press roll of the wet paper web transfer belt in all Examples and Comparative Examples; however, as shown in Table 2, cracks did not occur from the roll edge-facing regions and the boundary between the central region and the roll edge-facing region of Examples 1 to 7. It is understood that the effect of crack resistance was resulted from setting the difference in thickness between the thickness of the central region and the thickness of roll edge-facing regions to 0.5 mm or less and that maximum valley depth Rv of the outer circumferential resin layer surface of the roll edge-facing regions to 40 μm or less.

Moreover, the cracks of the boundary between the central region and the roll edge-facing region of Comparative Example 3 were worse than the cracks in Comparative Examples 1 and 2. The reason for this was that, as the difference in thickness between the central region and the roll edge-facing regions was large in this example, the repeated passage in particular of the guide rolls (front and rear side), the bending and curling impacted the roll edge-facing regions (in particular, the boundary between the central region and the roll edge-facing region).

DESCRIPTION OF THE REFERENCE CHARACTERS

20: Roll press surface (contacting surface), 21: Edge of the roll press surface (contacting surface), 31: Reinforcing fiber base material layer, 32: Outer circumferential resin layer, 33: Inner circumferential resin layer, 311: Reinforcing fiber base material, 312: Resin of the reinforcing fiber base material layer, 321: Resin of the outer circumferential resin layer, 322: Outer circumferential surface, 331: Resin of the inner circumferential resin layer, 332: Roll-contacting surface, 71: Roll, 72: Coater bar, 73: Resin discharge device, A: Central region, B: Roll edge-facing region, C: Edge region, D: Papermaking width, BR: Bearing, CY: Hydraulic cylinder, DA: Thickness of the central region, DB: Thickness of the roll edge-facing region, DC: Thickness of the edge region, DF: Dryer fabric, DI: Edge disk, GR: Guide roll, PM: Palm, PL: Fixing plate, PP1: First press part, PP2: Second press part, PF1, 2, 3: Press felts 1, 2, 3, PR1, 2, 3, 4, 5: Press rolls 1, 2, 3, 4, 5, PS: Shoe, SP: Shoe press belt, SH: Support shaft, SR: Suction roll, SW: Shower device, TB: Wet paper web transfer belt, WF: Wire, WW: Wet paper web. 

1. An endless wet paper web transfer belt travelling by rotation while being supported by a plurality of rolls in the press part of a papermaking machine; wherein the wet paper web transfer belt has at least an outer circumferential resin layer on the wet paper supporting side, the outer circumferential resin layer comprises roll edge-facing regions positioned to face both edges in the width direction of at least one of the plurality of rolls and a central region positioned between the roll edge-facing regions, the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.5 mm or less, and the maximum profile valley depth Rv of the outer circumferential surface of the roll edge-facing regions is 40 μm or less.
 2. The wet paper web transfer belt according to claim 1; wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is equal to the thickness of the central region.
 3. The wet paper web transfer belt according to claim 1; wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is smaller than the thickness of the central region.
 4. The wet paper web transfer belt according to claim 1; wherein a straight taper is provided from any position on the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.
 5. The wet paper web transfer belt according to claim 1; wherein an upward convex or downward convex curved taper is provided from any position on the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.
 6. The wet paper web transfer belt according to claim 1; wherein the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.3 mm or less.
 7. The wet paper web transfer belt according to claim 1; wherein the maximum profile valley depth Rv is 30 μm or less.
 8. An endless wet paper web transfer belt travelling by rotation while being supported by a plurality of rolls in the press part of a papermaking machine; wherein the wet paper web transfer belt has at least an outer circumferential resin layer on the wet paper supporting side, the outer circumferential resin layer comprises roll edge-facing regions positioned to face both edges in the width direction of at least one of the plurality of rolls, a central region positioned between the roll edge-facing regions, and edge regions positioned at the outside of the roll edge-facing regions, the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.5 mm or less, and the maximum profile valley depth Rv of the outer circumferential surface of the roll edge-facing regions is 40 μm or less.
 9. The wet paper web transfer belt according to claim 8; wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is equal to the thickness of the central region.
 10. The wet paper web transfer belt according to claim 8; wherein the thickness of the roll edge-facing regions of the wet paper web transfer belt is smaller than the thickness of the central region.
 11. The wet paper web transfer belt according to claim 8; wherein a straight taper is provided in any position from any position of the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.
 12. The wet paper web transfer belt according to claim 8; wherein an upward convex or downward convex curved taper is provided in any position from any position of the outer circumferential surface of the roll edge-facing region of the wet paper web transfer belt towards the edge of the wet paper web transfer belt in the opposite direction of the central region.
 13. The wet paper web transfer belt according to claim 8; wherein the difference in the thickness between the thickness of the roll edge-facing regions and the thickness of the central region is 0.3 mm or less.
 14. The wet paper web transfer belt according to claim 8; wherein the maximum profile valley depth Rv is 30 μm or less.
 15. The wet paper web transfer belt according to claim 1; wherein the above-mentioned at least one roll is a guide roll.
 16. The wet paper web transfer belt according to claim 8; wherein the above-mentioned at least one roll is a guide roll.
 17. The wet paper web transfer belt according to claim 1; wherein the above-mentioned at least one roll is a press roll facing the shoe of a shoe press device.
 18. The wet paper web transfer belt according to claim 8; wherein the above-mentioned at least one roll is a press roll facing the shoe of a shoe press device. 